Blue - I suggest you get some plywood for the floor and 1x10s for the walls. Make the box 3' - 4 ' square. on the sides, screw a 1x6 about 4" up from the floor on edge.Moms tend to roll on their sides during feeding and this protects the pups from being suffocated. And they like to snuggle under these boards.You should be able to get some sketches on line somewhere. If I find any, I will post them for you.